Index: trunk/ppStack/src/ppStackMatch.c
===================================================================
--- trunk/ppStack/src/ppStackMatch.c	(revision 20710)
+++ trunk/ppStack/src/ppStackMatch.c	(revision 20711)
@@ -47,5 +47,5 @@
 #endif
 
-bool ppStackMatch(pmReadout *readout, psArray **regions, psArray **kernels, float *chi2,
+bool ppStackMatch(pmReadout *readout, psArray **regions, psArray **kernels, float *chi2, float *weighting,
                   const psArray *sources, const pmPSF *psf, psRandom *rng, const pmConfig *config)
 {
@@ -384,4 +384,5 @@
         (void)psBinaryOp(readout->image, readout->image, "+",
                          psScalarAlloc(- psStatsGetValue(bg, PS_STAT_ROBUST_MEDIAN), PS_TYPE_F32));
+        *weighting = 1.0 / PS_SQR(psStatsGetValue(bg, PS_STAT_ROBUST_STDEV));
         psMetadataAddF32(readout->analysis, PS_LIST_TAIL, "PPSTACK.WEIGHTING", 0,
                          "Weighting by 1/noise^2 for stack",